JP2001153564A - Continuous heating furnace for substrate, utilizing radiant tube burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous heating furnace, capable of facilitating mass production, by a method wherein an energy cost is reduced while securing a temperature control accuracy required for the drying and firing of a substrate. SOLUTION: The continuous heating furnace for a substrate is provided with a plurality of heating chambers, having heating means at the upper part and the lower part of the same as well as a transfer means for transferring a matter to be heated into a neighboring heating chamber, and is constituted so as to be capable of effecting pre-heating, temperature raising, even heat retaining and cooling in accordance with a desired temperature curve by controlling the temperatures of respective heating chambers individually so that a substrate temperature enters within a predetermined temperature range. In the heating furnace 30, radiant tube burners 20 are employed for at least one side of the heating means at the upper part and the lower part of respective heating chambers 1-18 while electric heaters 21 are employed for the remaining heating means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a continuous heating furnace for heating a substrate such as a glass substrate for a plasma display panel.

[0002]

2. Description of the Related Art In recent years, large-screen flat panel displays (hereinafter, referred to as “FPDs”) that can be used as wall-mounted televisions and multimedia displays have been steadily put into practical use. Such a large-screen FPD is a self-luminous type having a wide viewing angle and good quality display, and has a quality advantage of a plasma manufacturing method that has a simple manufacturing process and is easy to increase in size. A display panel (hereinafter, referred to as “PDP”) is listed as a leading candidate.

As shown in FIG. 3, for example, a PDP is manufactured by using a thick film method in which printing, drying, and firing steps are repeated a plurality of times on the surface of a large glass substrate called a front glass or a rear glass, by using a thick film method. This is performed by sequentially forming various members such as phosphors and finally sealing the front glass and the rear glass.

[0004] In this case, it is required that the drying and firing of the glass substrate be performed in a state where the environment in the furnace is kept clean and the temperature of the glass substrate is precisely controlled so as to be as uniform as possible. . When drying and baking are performed in a state where the temperature distribution on the surface of the glass substrate is large, defects such as cracks, chips, and the like occur due to distortion of the substrate and the members formed on the substrate, and the yield of the product is reduced. This is because a defect occurs.

For this reason, conventionally, drying and firing of a large substrate such as a glass substrate used for a PDP is performed by heating an electric heater having a structure in which an Fe—Cr—Al-based electric heating coil is embedded in a ceramic fiber mold. A continuous heating furnace equipped with a plurality of heating chambers as means and a transfer means for transferring an object to be heated to an adjacent heating chamber is used, and each heating chamber is individually set so that the substrate temperature falls within a predetermined temperature range. By controlling the temperature in accordance with a desired temperature curve, preheating, heating, soaking, and cooling have been performed.
Electric heaters used as heating means are usually arranged in a matrix at the upper part (furnace ceiling) and the lower part (furnace floor) of each heating chamber so that the temperature distribution on the substrate surface is a predetermined value. The temperature of each of the divided heaters was individually controlled so as to fall within the range.

[0006]

[Problems to be solved by the invention] By the way, P
In disseminating the DP, it is an immediate task to reduce the cost higher than the CRT and to improve the mass productivity. However, in a conventional heating furnace using an electric heater as a heating means in the entire area of the furnace, energy costs are increased and a large-scale power supply for a factory is required, so that it is difficult to solve the above problem.

The present invention has been made in view of such a conventional situation, and an object thereof is to provide a PD
Drying of large substrates such as glass substrates used for P,
An object of the present invention is to provide a continuous heating furnace for a substrate capable of lowering energy costs and facilitating mass production while securing temperature control accuracy and cleanness of a furnace environment required for firing.

[0008]

Means for Solving the Problems According to the present invention, there are provided a plurality of heating chambers having heating means at an upper part and a lower part, and conveying means for conveying an object to be heated to an adjacent heating chamber,
By individually controlling the temperature of each heating chamber so that the substrate temperature falls within a predetermined temperature range, continuous heating for the substrate configured to perform preheating, heating, soaking, and cooling according to a desired temperature curve. In the heating chamber in the preheating / heating zone where preheating and heating are performed, a radiant tube burner is used in at least one of the upper and lower heating means, and the remaining heating means in the heating chamber are electrically powered. A continuous heating furnace for a substrate using a radiant tube burner characterized by using a heater is provided.

[0009]

As described above, in the continuous heating furnace for a substrate according to the present invention, a heating chamber in a preheating / heating region for performing preheating and temperature rising is provided in at least one of upper and lower heating means. A radiant tube burner was used, and the electric heater which was conventionally used for all the heating means was used only for the rest of the heating chamber. Thus, preheating
By using a radiant tube burner with a low running cost for more than half of the heating means in the heating chamber in the temperature increasing region, it is possible to reduce the energy cost of the entire furnace by half. In addition, since the electric heater is partially used, it is not necessary to prepare a large-scale factory power supply equipment as in the related art, and mass production becomes easier.

Further, the radiant tube burner is
Since the combustion is performed in the tube, the cleanness of the furnace environment required for drying and firing the large glass substrate for PDP can be easily ensured. Furthermore, since the radiant tube burner emits less carbon dioxide (CO ₂ ) than the electric heater, the radiant tube burner is also advantageous in terms of CO ₂ emission which is expected to become a problem in the future.

In the present invention, as shown in the following example, a radiant tube burner is provided for both upper and lower heating means in a preheating / heating area heating chamber for performing preheating and heating. For the heating chamber in the soaking zone and the cooling zone in the cooling zone for slow cooling, an electric heater is used for the upper heating means and a radiant tube is used for the lower heating means of the heating chamber. It is preferred to use a burner or an electric heater.

FIG. 1 is a schematic explanatory view showing an example of the structure of a continuous heating furnace according to the present invention in correspondence with a temperature curve (heat pattern) at the time of firing a large glass substrate for PDP. The continuous heating furnace 30 of the present example includes 18 heating chambers 1 to 18, of which 1 to 5 are heating chambers in a preheating / heating zone where preheating and heating are performed, and 6 to 10 are soaking chambers. The remaining heating chambers in the soaking zone for maintaining the temperature and the remaining heating zones 11 to 18 are the heating chambers in the cooling zone for performing the slow cooling.

The large glass substrate as the object to be heated is sent from the inlet of the continuous heating furnace into the furnace while being placed on a setter or the like, and is sequentially conveyed to the heating chamber adjacent to the outlet side by the conveying means. . Each of the above-mentioned heating chambers 1 to 18 has a heating means at an upper part (furnace ceiling) and a lower part (furnace floor), respectively, and a control system of these heating means makes a substrate temperature fall within a predetermined temperature range. By individually controlling the temperatures of the respective heating chambers, it is possible to preheat, raise the temperature, maintain a uniform temperature, and cool the large glass substrate according to a desired temperature curve. The number of heating chambers in the preheating / heating zone, the soaking zone, and the cooling zone and the total number of heating chambers are not particularly limited.

Further, it is preferable to use an intermittent feeding type conveying means for intermittently conveying the object to be heated to an adjacent heating chamber. Here, “convey intermittently” means that the object to be heated is kept stationary in the n-th heating chamber from the entrance side and heated for a predetermined time, and then the object to be heated adjoins as quickly as possible. This is a transport method in which the operation of moving from the entrance to the (n + 1) th heating chamber, heating the object to be stopped again, and heating for a predetermined time is repeated. The type of the transporting means is not particularly limited as long as such a transporting method is possible. For example, a walking beam may be used, or a roller or a conveyor may be intermittently driven.

In the present embodiment, heating chambers 1 to 5 in a preheating / heating region
The radiant tube burner 20 is used for both the upper and lower heating means, and the heating chambers 6 to 10 in the soaking zone and the heating chambers 11 to 18 in the cooling area are electrically heated by the upper heater. 21, a radiant tube burner 20 is used for the lower heating means.

As described above, drying and baking of a large-sized substrate such as a glass substrate used for a PDP must be performed in a state where the temperature of the substrate surface is precisely controlled so as to be as uniform as possible. However, in practice, equal precision is not required for all heating steps,
The accuracy of temperature control required for preheating and temperature raising is somewhat less strict than for soaking and gradual cooling.

Specifically, a PDP of 50 to 60 inches
Temperature difference Δt between the maximum temperature and the minimum temperature at each part of the substrate surface of the large glass substrate for
Within ２０20 ° C, 500-600 ° C in preheating / heating region of ℃
In the soaking zone, within Δ6 ° C, preferably within Δ3 ° C,
In the cooling range of 600 to 400 ° C., the temperature is within Δ6 ° C.

Therefore, in the present embodiment, the required accuracy of the temperature management is relatively moderate, and the heating chambers 1 to 5 in the preheating / heating region, which consume the most energy, have a higher temperature than the electric heater. The radiant tube burner 20, which is inferior in management accuracy but has low running cost required for heating, is used for both upper and lower heating means. In addition, for the heating chambers 6 to 10 in the soaking zone and the heating chambers 11 to 18 in the cooling zone where strict temperature control accuracy is required, the electric heater 21 is used only for the upper heating means, and the lower heating means is used for the lower heating means. The radiant tube burner 20 was used similarly to the heating chamber in the preheating / heating region.

In the heating chambers 6 to 10 in the soaking zone and the heating chambers 11 to 18 in the cooling zone, the lower radiant tube burner 20 performs rough heating while the upper electric heater 21 performs fine temperature control. By doing
Ensure the temperature control accuracy required for drying and firing the substrate.

FIG. 2 is a schematic explanatory view showing an example of a heating chamber in a preheating / heating region. The heating chamber is partitioned by a partition 23. The partition 23 preferably has a minimum opening that does not hinder the transfer of the substrate 25 when the substrate 25 placed on the setter 24 is transferred to an adjacent heating chamber. Further, in the present invention, it is preferable that the radiant tube burner 20 used as a heating means of the heating chamber in the preheating / heating zone be installed on the inlet side of the furnace with respect to the center of the heating chamber.

That is, in the preheating / heating region, the temperature of the heating chamber closer to the inlet of the furnace is set lower, and
Since the object to be heated is conveyed from a lower temperature heating chamber to each heating chamber, the temperature of the inlet side is low and the temperature of the outlet side is high in each heating chamber under the influence of the temperature of the adjacent heating chamber. Tend to be. As described above, the radiant tube burner 20 is installed closer to the inlet side of the furnace than the center of the heating chamber, and the heating source is brought closer to the inlet side of each heating chamber where the temperature tends to be low, so that the temperature distribution in each heating chamber can be improved. Can be reduced.

In the continuous heating furnace of the present invention, it is preferable that a muffle is arranged between the heating means and the moving area of the object to be heated. As for the muffle, it is preferable to use a material made of a light non-transmissive material having high thermal conductivity in a portion where a radiant tube burner is used as a heating means. As a specific material, a material close to a black body is desirable.For example, a molded body containing silicon carbide and carbon as main components is formed by reducing a metallic silicon in a reduced-pressure inert gas atmosphere or vacuum where metallic silicon is present. Si-impregnated SiC obtained by firing while impregnating is included. With a muffle made of such a material, since far-infrared rays or near-infrared rays are irradiated from the muffle by once receiving the heat generated from the radiant tube burner, it is possible to heat the object to be heated more quickly. .

On the other hand, a muffle made of a light-impermeable and high-thermal-conductivity material may be used for the portion where the electric heater is used as the heating means, as described above. Preferably, it is used. A specific material is, for example, crystallized glass.
When a muffle made of such a light-transmitting material is used, an object to be heated can be quickly heated by an electric heater. Further, by airtightly separating the heating means and the object to be heated by such a muffle, an effect of improving the cleanliness in the moving region of the object to be heated can be obtained.

[0024]

As described above, the continuous heating furnace for a substrate of the present invention using a radiant tube burner has the following features.
The energy cost required for drying and firing the substrate is halved compared to a conventional continuous heating furnace that uses only an electric heater as the heating means. As a result, substrates such as glass substrates for PDPs can be made more inexpensive. Can be provided. Also,
Since the electric heater only needs to be partially used, it is not necessary to prepare a large-scale power supply for a factory as in the related art, and mass production becomes easier.

Furthermore, in the present invention, the radiant tube burner used as a heating means other than the electric heater can burn the inside of the tube, so that a clean furnace environment can be easily ensured and CO 2
_{(2) Since the} amount of emission is smaller than that of the electric heater, it is more advantageous than the conventional heating furnace in terms of the amount of CO ₂ emission which is expected to be a problem in the future.

Furthermore, by installing the radiant tube burner in the heating chamber in the preheating / heating zone at a position closer to the inlet of the furnace than the center, the temperature distribution in each heating chamber and the temperature distribution on the substrate surface can be reduced. In addition, it is possible to prevent the substrate from being distorted and defects such as cracks and chips resulting therefrom, thereby improving the product yield.

[Brief description of the drawings]

FIG. 1 shows an example of a structure of a continuous heating furnace according to the present invention using a PD.
It is the schematic explanatory drawing shown corresponding to the temperature curve at the time of baking of the large glass substrate for P (heat pattern).

FIG. 2 is a schematic explanatory view showing an example of a heating chamber in a preheating / heating region.

FIG. 3 is a process diagram showing a PDP manufacturing process.

[Explanation of symbols]

1-5: Preheating / heating zone, 6-10: Heating zone, 11-18: Cooling zone, 20: Radiant tube burner, 21: Electric heater, 23: Partition wall, 24: setter, 25: substrate, 30: continuous heating furnace.

Claims (6)

[Claims] A plurality of heating chambers each having heating means at an upper portion and a lower portion; and a transporting device for transporting an object to be heated to an adjacent heating chamber, wherein each substrate has a temperature within a predetermined temperature range. A continuous heating furnace for a substrate configured to perform preheating, heating, soaking, and cooling according to a desired temperature curve by individually controlling the temperature of the heating chamber, wherein the preheating and the heating are performed. The radiant tube is characterized in that a radiant tube burner is used for at least one of the upper and lower heating means in the heating chamber in the preheating / heating area to be performed, and an electric heater is used for the remaining heating means in the heating chamber. Continuous heating furnace for substrates using burners. 2. A heating chamber in a preheating / heating area for performing preheating and temperature raising, wherein a radiant tube burner is used for both upper and lower heating means, and a soaking area for heat equalization is provided. 2. The substrate according to claim 1, wherein an electric heater is used for an upper heating means in the heating chamber and a heating chamber in a cooling zone for performing slow cooling, and a radiant tube burner or an electric heater is used for a lower heating means in the heating chamber. For continuous heating furnace. 3. The continuous heating furnace for a substrate according to claim 1, wherein a muffle made of a light-impermeable and high-thermal-conductivity material is arranged between the heating means and the moving area of the object to be heated. 4. A muffle made of a light non-transmissive and high heat conductive material is disposed between the heating means and the moving area of the object to be heated in a portion where a radiant tube burner is used as the heating means. 3. The continuous heating furnace for a substrate according to claim 1, wherein a muffle made of a light-transmitting material is disposed between the heating means and a moving area of the object to be heated in a portion where the electric heater is used as the means. 5. The radiant tube burner has a preheat
The continuous heating furnace for a substrate according to any one of claims 1 to 4, wherein the continuous heating furnace is provided on a heating chamber in a temperature-raising region closer to an entrance of the furnace than a center portion. 6. A continuous heating furnace for a substrate according to claim 1, wherein said transfer means is a transfer means of an intermittent feed system for transferring a heated object intermittently to an adjacent heating chamber. .